Signaling system



July 26, 1932.

H. E. OVERACKER SIGNALING SYSTEM Filed May 21, 1928 2 Sheets-Sheet l INVENTOR. y ifovenzc/fer A TTORNE YS.

July 26, 1932.

H. E. OVERACKER 1,868,614

SIGNALING SYSTEM Filed May 2l,-l928 2 Sheets-Sheet 2 Ems/n22,-

M tor INVENTOR. By HAETOrerac/fer A TTORNEYS.

Patented July 26, 1932 UNITED STATES PATENT OFFICE HORACE E. OVERACKER', OF PALO ALTO, CALIFORNIA, ASSIGNOR TO FEDERAL TELE- GRAPH COMPANY, OF SAN FRANCISCO, CALIFORNIA, A CORPORATION OF CALI- FORNIA SIGNALING SYSTEM Application filed. May 21, 1928.

This invention relates to carrier wave receiving systems and particularly to radio telegraph receiving systems.

An object of the invention is to effectively amplify weak carrier wave signals.

Another object is to modulate and thereby make audible continuous wave telegraph signals.

A feature of the invention is a radio receiving circuit comprising a cold electrode gaseous discharge device for modulating a received wave at a frequency intermediate audio and radio frequencies.

The system of the invention resembles a conventional double detection system to this extent, that in both systems high gain is obtained by amplifying the signal at a frequency above the usual audio range and below that of the received radio wave. It differs from the conventional double detection system in that the wave of intermediate frequency is obtained by periodically varylng the resistance of the receiving circuit at the intermediate frequency, instead of superimposing on the incoming wave a locally generated wave differing in frequency therefrom by the frequency of the desired intermediate wave.

In the drawings:

Figs. 1 and 2 are circuit diagrams of two systems in accordance with the invention Referring to Fig. 1 of the drawings, I have shown an electrical circuit 10 excited from some suitable source of signal energy at carrier frequency, such as the radio antenna 11. The circuit 10 forms the input circuit of an electron relay 12 and is tuned to the carrier frequency of the energy recelved by means of an inductance 13 shunted by a variable capacitance 14:. A variable tuning condenser 16 is also preferably inserted in series with antenna 11. The output circuit of relay 12 is connected with further amplifying devices as will be presently explained, and is also preferably provided with a controlled feed-back circuit in order to provide utmost sensitivity. As a feedback circuit, I have shown an inductance 17 having one terminal connected with the plate or anode of relay 12, and the other terminal connected to the oath- Serial No. 279,291.-

ode of relay 12 thru a variable capacitance 18. Inductance 17 is coupled to inductance 13, and the degree of feed-back is controlled by variable condenser, 18 in order to secure the desired amount of regeneration. The input circuit to the relay includes the usual grid condenser 19 and grid leak 21, as relay 12 is operated as a detector.

In order to modulate the received wave in circuit 10 I employ a gas discharge tube 26 which is excited and associated with circuit 10 in such a manner as to repeatedly vary the resistance component of this circuit. The particular type of gas discharge tube preferably employed utilizes cold electrodes, and contains gas under low pressure which may be readily ionized. Such gas discharge tubes are well known in the art and contain gases such as neon, helium, argon, crypton, zenon andthe like, or mixtures thereof.

Such a gas discharge tube is associated with the circuit 10 by connecting the electrodes of the tube across two points of different potential, and good results have been obtained by utilizing points located along the inductance '13. Thus the anode 27 of tube 26 is shown connected to an intermediate tap 28 on inductance 13, while the other electrode, cathode 29, is connected to the low potential terminal of inductance 13. A condenser 31 is inserted in series with the tube and tap 28 for a purpose to be later explained.

It is characteristic of a cold electrode gas discharge tube that no dischargewill take place between its electrodes until the applied potential is increased above a given critical value, after which the resistance is broken down and a current discharge takes place. In my system the resistance of the gas discharge tube 26 is repeatedly broken down by exciting the tube from a pulsating or alternating current, or the tube may be caused to oscillate by means of a suitable exciting circuit. I prefer to'operate the tube in oscillating condition, and forthis purpose there is shown an exciting circuit consisting of a source of direct current potential 33 connected across the electrodes of tube 26 in series with a relatively high resistance 84. It is commonly known that with such an exciting circuit a gas discharge tube will oscillate at a frequency depending in part upon the value of the resistance 34:, and upon the characteristics of the relay. The frequency of oscillations can be readily controlled by inserting a variable condenser across the electrodes of the tube, or by inserting a variable condenser 36 in shunt with the high resistance 34. One side of the tube 26 is connected to a point of neutral potential as by means of ground connection 37, which also serves as aground for the cathode of relay 12. Condenser 31 serves to pass radio or carrier frequency currents from circuit 10, but serves to block the lower frequency oscillatory currents set up in the exciting circuit for tube 20. A radio frequency choke 38 is inserted in series with anode 27, in order to block radio frequency currents which might otherwise flow thru condenser 30 to the ground 37.

'1 preferably operate tube 26 at a fundamental frequency relatively high compared to the ordinary sound frequency, say from 10,000 to 50,000 cycles, and at a frequency substantially lower than the carrier frequency of received signals. It is apparent that when the resistance of tube 20 is broken down at a frequency of say 20,000 cycles, the signal energy in circuit and likewise the re peated signal energy in the output circuit of relay 12, is modulated at a frequency of 20,000 cyclcs,because of the repeated variation in the resistance component of circuit 10. In my system I select out and further amplify energy of the frequency at which tube is operated. For this purpose I have shown suitable filter means d1 adapted to receive. energy from the output circuit of relay 12, and serving to pass energy of the desired fre quency to a further amplifier relay 22. Any suitable form of filter means 41 may be employed which will secure proper filter action and for this purpose I have shown a transformer having tuned primary and secondary windings. The primary winding has a center tap 42 connected to a high potential point of the output of relay 12. For example tap 42 is shown as connected to a point intermediate inductance 17 and variable capacitance 18, in series with a suitable radio or carrier frequency choke 13. The 13 battery 1 1 in the output circuit of relay 12 may be connected in series with the primary of transformer 11 as shown, the other terminal of this battery being grounded. Energy from the output circuit of relay 22 may be passed thru another filer L6, and again amplified in another amplifier 47, after which it is applied to a second detector or integrating device 48. The output circuit of detector 18 is shown connected to a translator 51 through an audio frequency amplifier 4-9. If signals are being repeated with a tone frequency, an-

, other filter 52, tuned to the tone frequency,

is preferably inserted between detector -18 and amplifier 49.

To explain the operation of the above system, it will be presumed that the gas discharge. tube 20 is being operated in such a. manner that its resistance is broken down at a rate equal to say 20,000 cycles. This serves to short circuit, for radio frequency current, the lower turns of inductance 13 through condenser 31 and tube 26, and part of the radio frequency energy received from antenna 11. is dissipated. The net effect of varying the resistance of tube is to vary the amplitude of, and thus modulate at 20,- 000 cycles, the waves received from antenna 11 and applied to the input circuit of tube 12. Detector tube 12 demodulates the wave and the resultant 20,000 cycle component is selected by the tuned circuits associated with filter ll and further amplified. As waves of such a frequency are readily amplifier, signal energy of this frequency can be built up to any desired intensity by repeating thru any number of amplifier stages. After being sufficiently amplified, the 20,000 cycle wave is rectified in the second detector 18. If the received signal is modulated with a. wave of tone frequency, the 20,000 cycle com ponent in the output circuit and detector 12 will carry the tone modulation and after detection in the second detector 18 the tone wave will be selected by filter 52, further amplified by amplifier l9, and applied to the translator 51 I'Vhen utilizing my system for the reception of continuous wave signals, it is preferable to provide some local means for interrupting the signal energy at a tone frequency. As an added feature to the system shown in Fig. 1, I provide means for effecting this result in the form of another gas discharge tube 53. This tube is provided with a suitable enciting circuit consisting of battery and resistance 54 shunted by variable capacitance Tube 53 can be connectedacross the same points of the inductance 13, to which tube 26 is connected. The characteristics of tube 53, and the value of condenser 56 and resistance 5 1 are preferably such that the resistance of tube is broken down at an audio frequency, or tone frequency. Thus with both tubes 20 and operating to mode ulate the received energy in circuit 10, the wave selected by filter means -11 and which has a frequency to which tube 26 is operating, is modulated by the tone frequency of tube 53. Filter is preferably tuned to this tone frequency so as to render the system more selective and less subject to interference.

The distinction between the circuit of Fig. 1 and a conventional double detection of super-heterodyne circuit should be carefully noted. The gas discharge tube 20 does not generate a wave which is superimposed on the received wave and modulated therewith in detector tube 12. Condenser 31 effectively prevents the transfer of energy of 20,000 cycles from the local oscillator comprising tube 26 to tube 12. When no wave is being received by antenna 11, no oscillations occur in circuit 10, tube 12 is inactive, and the translator 51 does not respond to the oscillations generated in tube 26. When waves are received by antenna 11 they are modulated at 20,000 cycles by the impedance changes in circuit 10 before being applied to tube 12. The latter functions simply to demodulate a single, modulated wave, not to modulate two distinct waves as does the first detector in the conventional double detection circuit.

A modification of the invention has been shown in Fig. 2, in which only one neon tube has been shown for producing an intermediate amplifying frequency. Instead of connecting the gas discharge tube circuit across a small portion of the inductance 13, in this instance I have shown the anode 27 connected directly to the high potential side of inductance 13, in series with condensers 31. A radio frequency choke 53 is connected between the grounded side of the gas discharge tube circuit and the connection between condensers 31. By means of this arrangement of condensers 31 and choke 53, currents generated in the neon tube exciting circuit are prevented from being fed into the input circuit of tube 12, although recurrent changes in resistance of gas discharge tube 26 serve to recurrently vary the resistance component of the input circuit to tube 12.

Where a single gas discharge tube is employed as with the system of Fig. 2, the system is adapted for the reception of signals modulated by a tone frequency. In case continuous wave telegraphic signals are received, in the absence of gas discharge tube 53 incorporated as described with reference to Figure l, I utilize some other means associated with the receiver for effecting modulation of the received energy by a tone frequency. This can be accomplished by the use of suitable interrupting means or a chopper imposed in the receiver before the translator, or by some form of recurrently varying reactance. In Fig. 2 I have shown the use of a periodically varying condenser 56, driven by means of motor 59, and associated with the intermediate frequency circuits of the amplifier tube 22. In this instance in order to make the condenser 56 more effective, I have shown the same in series with a regenerative feed back coil 57. Variable condenser 56 is preferably shunted by means of another condenser 58. When in operation amplifier tube 22 is adjusted so as to operate regeneratively. Upon rotation of condenser 56, the degree of feed back afforded by coil 57 is recurrently varied and therefore the amplifying eificiency of tube 22 is repeatedly varied at a tone frequency. As a result energy repeated thru tube 22 is modulated by a tone frequency, depending upon the rate of rotation of condenser 56, and this tone frequency operates translator 51. The system as shown in Fig. 2 has been found to be more stable in operation and is therefore to be preferred to the system of Fig. 1.

I claim:

1. In a. signaling system, a circuit coupled with a source of signal energy of carrier frequency, a. gas discharge tube connected across points of different potential of said circuit, means for exciting said tube whereby its resistance isrepeatedly broken down at a frequency differing from said carrier frequency, and filter means adapted to receive energy from said circuit tuned to pass the frequency with which energy is modulated by the breaking down of the resistance of said tube.

2. In a radio telegraph receiving system, a source of continuous wave signals, a first detector having an input circuit associated with said source, and an output circuit, means for periodically varying the impedance of a portion of said input circuit at an intermediate frequency lower than the frequency of said continuous waves but above audibility, second means for simultaneously varying the impedance of a portion of said input circuit ata tone frequency, filter means in the output circuit of said first detector selective to said intermediate frequency, a second detector coupled to said filter means, and means connected to said second detector responsive to said tone frequency.

In testimony whereof, I have hereunto set A my hand.

HORACE E. OVERACKER. 

